Resting-, variation- and action potentials and their contribution to photoperiodic control of flowering
Wagner, E., Normann, J., Albrechtová, J.T.P., Bonzon, M., Greppin, H.
Institut für Biologie II, Universität Freiburg, Schänzlestr. 1, D-79104 Freiburg, Germany
To study the inter-organ communication between the signal-perceiving organ (leaf) and the target tissue (stem/apex) implied in the control of flowering rhythmic kinetics of stem extension rate (SER) and leaf movement (LM) were investigated in the short-day plant Chenopodium rubrum (C. r.) and in the long-day plant Chenopodium murale (C. m.). To observe whole plant behaviour time laps photography was used showing rhythmic integration of the main shoot axis and side branches in rhythmic growth as well as in leaf movements. SER was continously monitored using an auxanometric system while simultaneously analyzing LM via a video system. Cytoplasmic pH at the apical meristem was analysed using confocal laser scan microscopy and fluorescent dyes. Changes in organ surface potentials were investigated using bipolar recordings with surface platinum electrodes.
Both species exhibit circadian rhythms in SER and LM, flowering plants showing significantly shorter period lengths. While in vegetative plants (C. m.) the kinetics of SER and LM are 180° out of phase this phase relationship is shifted after flower induction. Both parameters display clear movement and growth patterns with photoperiod-specific reactions to ‘light-on’ and ‘light-off’ signals. Flower induction correlates to a threshold value for the ratio of the integral growth during the dark span over the integral growth in the light span. Two hours after the end of the critical dark period the pattern of cytoplasmic pH at the apical meristem is changed possibly indicating the arrival of the inductive signal.
Rhythmic integration over the whole plant possibly involves modulation of turgor pressure via stretch activated ion channels and concomitant changes in membrane potential. They might trigger cytoplasmic changes in pH at the shoot apex as secondary messengers in photoperiodic signal transduction. Finally the switch from the vegetative to the flowering state is a threshold response, systemic in nature and involving not only the apical meristem but also the axillary buds.
[1] Wagner, E., Normann, J., Albrechtová, J.T.P., Bonzon, M., Greppin, H. (1997) Photoperiodic control of flowering: Electrochemical-Hydraulic communication between plant organs - “Florigen” a frequency-coded electric signal? In: H. Greppin, V. Penel, P. Simon, eds, Travelling Shot on Plant Development. Geneva Univ. Press.
[2] Albrechtová, J.T.P., Slavik, J., Wagner, E. (1997) Confocal pH-topography in the shoot apex of Chenopodium rubrum in relation to different photoperiods. Endocytobiosis & Cell Res. 12: 83-94
| LOCATION |
DATE |
TIME |
| Lecture Hall II |
Thursday, April 9 |
03:00 pm |